A conventional frequency multiplier circuit device is an analog circuit as disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 7-231223, which comprises an n.multidot.m-stage ring counter 30 as shown in FIG. 1. A phase comparator 2 receives a reference input signal REF INPUT SIGNAL from an input signal terminal 1 and an output signal from the n.multidot.m-stage ring counter 30. It compares the phases of the received two signals and controls, so that the phases of the two signals coincide, a propagation delay time of the counters of the respective stages of the n.multidot.m-stage ring counter 30 by means of an output voltage from an LPF (Low Pass Filter) 4.
The n.multidot.m-stage ring counter 30, as shown in FIG. 2, comprises an n-number of flip-flops (FF1, FF2, . . . FFn). An output from the last stage is returned to the first stage, thus forming a ring counter. The propagation delay times of the counters of the respective stages can be changed by a control voltage.
When the phase of the reference input signal coincides with that of the n.multidot.m-stage ring counter 30, a signal is extracted from middle stages of the n.multidot.m-stage ring counter 30, thereby generating a signal having a phase shifted from a phase of the reference input signal REF INPUT SIGNAL.
The generated signal is exclusive-NORed by a logic circuit 5, so that a high frequency-multiplied signal with respect to the reference input signal REF INPUT SIGNAL can be output from an output terminal 6.
However, since the conventional frequency multiplier circuit device is constituted by an analog circuit, an LPF 4 is required to form a semiconductor device using the frequency multiplier circuit device. For this reason, it is difficult to incorporate an LPF 4 into an LSI semiconductor substrate using a gate array or the like.
Therefore, according to the conventional art, it is necessary to attach an LPF to an exterior of the LSI semiconductor substrate.
Accordingly, a circuit board requires an area on which an LPF 4 is to be mounted, with the result that the board area is increased. In addition, since a control voltage of an analog quantity is used, the frequency multiplier circuit device is liable to be influenced by a power source noise, so that an output signal may be easily fluctuated. Because of these drawbacks, the conventional frequency multiplier circuit device has only limited uses.